Motor control system



A. F. KENYON MOTOR CONTROL SYSTEM Nov. 16, 1948.

Filed Aug. 22. 1946 INVENTOR /7/0/) 20 FA en yon.

I TTO RN WITNESSES.

(5a ,7 Y r\ Patented Nov. 16, 1948 MOTOR CONTROL SYSTEM Alonzo F. Kenyon, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application August 22, 1946, Serial No. 692,339

8 Claims.

My invention relates, generally, to control systems, and it has reference, in particular, to motor control systems.

Generally stated, it is an object of my invention to provide a motor control system that is simple and. inexpensive to manufacture, and is reliable and efiicient in operation.

More specifically, it is an object of my invention to provide for matching the speed of a feed roll motor in a rolling mill with the speed of the main roll motor over a wide range of speeds and under varying load conditions.

Another object of my invention is to provide for so controlling the excitation of a control generator in a control system for a motor as to obtain substantially the same percentage of speed regulation with the motor at difierent speeds.

Another object of my invention is for controlling the operation of a plurality of auxiliary motors in accordance with the operation of a main motor by using a pilot generator driven by the main motor, and whose excitation is difierentially responsive to the load on the auxiliary motors.

It is an important object of my invention to provide for producing a drooping load characteristics in a motor so as to obtain substantially the same percentage of speed regulation at different speeds.

A further object of my invention is to provide for differentially exciting a pilot generator driven by a main roll motor in accordance with the load on a feed roll motor and for energizing the feed roll motor in accordance With the output of the pilot generator and the load on said motor.

Yet another object of my invention is to provide a speed matching system for a pair of motors wherein the motor whose speed is controlled to match its speed with that of the other motor is given a steeply drooping speed-load characteristic with substantially the same percentage of regulation at all speeds.

Other objects will in part be obvious, and will in part be described hereinafter.

In practicing my invention, in one of its forms a feed roll motor in a rolling mill is energized from a generator whose output is controlled by a control generator having field windings energized in accordance with the feed roll motor current and in accordance with the output of a pilot generator driven by the main roll motor. A drooping speed regulation characteristic is provided which produces substantially the same percentage of speed regulation for the feed roll motor at all speeds by using a differential field Winding on the pilot generator which is energized in accordance with the feed roll motor current and whose connections are reversed whenever the main roll motor is reversed.

For a more complete understanding of the nature and scope of my invention, reference may be made to the following detailed description which may be studied in connection with the accompanying drawing, in which:

Figure l is a diagrammatic view of a motor system embodying the invention in one of its forms, and

Fig. 2 shows curves illustrating the speed regulation characteristics of the feed roll motor under varying load conditions.

Referring to Figure l, the reference numeral l may denote generally a motor system wherein a main motor l2 having an armature l3 and a field winding l4 may be connected to reversibly drive a load such as the main rolls I5 of a rolling mill. Auxiliar motors 1-6 and- Il may be used in association with the main motor to drive means operable in accordanc with the speed of the main motor, such as, for example, feed rolls [9 and '20 which may be positioned ahead of and behind the main rolls for feeding material to and from the rolls IS in opposite directions,

The field winding M of the main roll motor may be excited from any suitable, controllable source of electrical energy. The armature I3 may be energized from a variable voltage source, being for example connected in circuit with the armature 2 l of a main generator 22 having a field winding 23. The speed of the main motor l2 may be controlled by varying the excitation of the generator field winding 23 from a suitable source of electrical energy through suitable control means represented by the rheostat 24. Reversal of the main roll motor I2 may be effected by operatively connecting the field winding 23 to the generator 22 in opposite senses through one or the other of forward and reverse switches 25 and 26 under the control of manual forward and reverse control switches 28 and 29, respectively.

Operation of the feed roll motors l6 and i 1 may be efiected by connecting their armatures 30 and 3| in circuit with the armatures 33 and 3.4 of auxil-iary generators 35 and 36, respectively. The.

field windings 31' and 38 of the feed roll motors may be energized from a suitable source of sub stanti-ally constant voltage. The auxiliary generators may be driven by means of auxiliary motors 40 and 42, which may, for example, be energized from a suitable source of alternating current through any suitable control means, so as to start them when the main motor I 2 is started.

In order to provide for controlling the speeds of the feed roll motors it and ll, means such as the control generators 34 and 55 may be used to energize the field windings 46 and ill of the auxiliary generators 35 and 3t, respectively. The armatures 48 and 49 of the control generators 44 and 45 may be connected in series circuit relation with the field windings it and 41 of the auxiliary generators and self-energizing series field windings 56 and 5!, respectively. The control generators may also be provided with IR drop compensation field windings 52 and 53 which may be energized in accordance with the armature currents of their respective feed roll motors It and Il to produce more accurate speed matching at low speeds. They may, for example, be connected across resistors 54 and 5% connected in the armature circuits of the feed roll motors i6 and H, respectively. Control field windings 51 and 58 may also be provided on the control generators, being connected across the armatures of the feed roll motors and/or IR drop compensation field winding.

In order to provide for controlling the operation of the feed roll motors to and ii in predetermined relation with speed characteristics of the main roll motor E2, the control generators 44 and to may be provided with pattern field windings 60 and 65, respectively, which provide the principal excitation of the control generators, and oppose the control field windings. Energization of these field windings may be effected by means of pilot generators 6G and El which may be operated in accordance with the speed of the main motor, being, for example, driven by the main roll motor [2. The pilot generators may be provided with main field windings E39 and it which may be connected to a suitable source of electrical energy, and differential field windings l2 and l? for producing a drooping speed regulation characteristic. These windings may be energized in accordance with the load on the respective feed roll motors. The field windings l2 and '33 may, for example, be connected across the resistors 54 and 55 in the armature circuits of the feed roll motors it; and ii, respectively.

In order to provide for securing the same differential eliect on the energization of the pattern field windings and iii, even though the direc tion of operation of the pilot generators and hence the output, reverses when the main roll motor i2 is reversed, means such as the forward switch means 55, it and reverse switch means ll, 78 may be provided for reversing the connections of the differential field windings l2 and ":3 through contact members a, 15b, Etc, 761) and Ho, lib, 18a, liib, so as to maintain the same relative polarities under reverse operating conditions. Operation of the switches l5, l6 and ll, it may be effected by connecting their respective operating windings 19, 8B and iii, 82 for energization under the control of the manual control switches 23 and 29, respectively.

Since the speeds of the feed rolls l9 and 2t must necessarily be difierent owing to the reduction in thickness of material being rolled between the main rolls l5, draft control means comprising rheostats B5 and 36 may be connected in circuit relation with the pattern field windings G0 and SI of the control generators ts and 45, respectively. Contact members We and E60 of the reverse and forward switches Ti and it, respectively, may be used to shunt the draft control rheostats 85 and 8G to change the relative speeds ofthe feed roll motors, depending on their direction of operation. Roll diameter control rheostats 8i? and 88 may also be provided for changing the relative speeds of the feed roll motors in accordance with differences in the relative diameters of the feed rolls and main rolls.

In operation, the forward manual control switch it may be closed to effect operation of the forward control switch 25 for connecting the field winding of the main generator to the source, whereby the armature d3 of the main r011 motor may be energized to operate the rolls it; of roll material in the forward direction proceeding from left to right.

The motors ill and 12 may be started in any suitable manner. Upon operation of the switch the operating windings l9 and 86 of the forward control switch it; and it are also energized. The difierential field winding if; of the pilot generator 86 will thus be connected across the control resistor 58 through contact members 15a 15b of the forward control switch means it in such a direction as to be differential with respect to the field winding 69. The difierential field winding l3 of the pilot generator 61 will likewise be connected through contact members lfia and it?) of the forward control switch it to the control resistor 5% in such a sense to be difierential with respect to the main field windil'lg it. The draft control rheostat 86 of the pattern field {i l will be shunted by contact member Jtc, while the draft control rheostat remains connected in circuit with the pattern field 63. Accordingly the excitation of the pattern field winding 6i will be greater than that of the pattern field winding 58, thus increasing the net ex citation of the control generator 45 relative to that of the control generator M, and increasing the speed of the feed roll motor ll relative to the speed of the feed roll motor it to accommodate the increased speed of the material being rolled as it leaves the rolls.

When the main roll motor i2 is reversed by opening the forward manual control switch 28 and closing the reverse manual switch 29, the switches 25 and are energized and deenergized respectively. The motor l2 reverses, reversing the direction of rotation of the pilot generators lit and El. JThe control switches l5, it are deenergized and the control switches ll, 18 are energized. The connections oi the differential field windings "l2 and "E3 of the pilot generators are therefore changed to maintain differential relations with the main field windings 59 and 10, despite reversal of output of the auxiliary generators and 3i) due to reversal of the output of the pilot generators t6 and El. The draft control rheostat 8-5 is now shunted by the reverse switch ii to increase the speed of the roll motor 9 3 relative to the roll motor ll.

During operation in either direction. an increase in load on either one of the feed roll motors H3 or H results in an increase in the drop across the resistor 54 or 55 and an increase in the excitation of the respective dififerential field winding l2 or E3 of the pilot generator $6 or ill, as well as an increase in the excitation of the control generator IR drop compensating field winding 52 or 53. Accordingly the output of the particular pilot generator will be reduced, while the output of the particular control generator will tend to increase due to increased excitation of its IR drop compensating winding 52 or 53. Since the pattern field windings (ill and iii energized from the pilot generators are cumulative with respect to the principal excitation of the control generators, the output of the particular control generator affected is modified thereby, sothat the speed of the respective feed roll motor energized in accordance therewith is also modified.

Thus the speed matching function of the system is modified by a drooping speed regulation characteristic. This arrangement has the particular advantage that at low speeds the effect of the difieren-tial field Winding of the pilot generator is small, due to the low speed of the pilot generators. Since the pilot generator outputs vary with their speed, as well as with the loads on-their associated-feed roll-motors, the modification is less at low speeds, and substantially the same percentage of speed regulation is obtained at all speeds, instead of the same actual speed regulation. This is shown by the curves A and B of Fig. 2, which represent speed regulation curves obtained by practicing my invention at 100% and 25% speeds, respectively. It will be seen that the amount of droop is proportional to the speed, as well as to the load.

From the above description and the accompanying drawing, it will be seen that I have provided a simple and effective speed matching system wherein substantially the same percentage of speed regulation is obtained at all motor speeds. A system embodying my invention avoids interconnection of the variable voltage systems with the field excitation system, hence reducing the probability of false operation in service. Accurate speed matching of the feed roll and main mill motors at all speeds is obtained by using a pilot exciter whose output is directly proportional to the main mill motor and differentially proportional to the feed motor load, to provide a drooping speed and load characteristics for the feed roll motor which is variable for different speeds and diiierent loads.

Since certain changes may be made in the above described construction and diiferent embodiments of the invention may be made without departing from the spirit and scope of the invention, it is intended that all the matter contained in the above description and shown in the accompanying drawing shall be considered as illustrative, and not in a limiting sense.

I claim as my invention:

1. In a control system for controlling one motor in accordance with the speed of another motor,

control means producing a control voltage differentially responsive to the speed of said another motor and the load on said one motor, and generating means connected to supply electrical energy to said one controlled motor in accordance with said control voltage and the load on said one controlled motor.

2. A control system for a motor comp-rising, a pilot generator responsive to a predetermined speed condition, excitation means connected to vary the output of said pilot generator inversely with variation of the load on said motor, and circuit means including a regulating generator responsive to the output of the pilot generator and the load on said motor connected to apply a variable control voltage to said motor.

3. A speed matching system for controlling the speed of one motor in accordance with the speed of another motor comprising, a pilot generator responsive to the speed of said another motor, excitation means varying the output of the pilot generator in the opposite sense to variations in the load on said one controlled motor, and a regulating generator responsive to the output of the pilot generator and the load on said one motor connected to control the supply ofelectrical energy to said one controlled motor.

4. A control system for controlling one: motor in accordance with the speed of another motor comprising, a pilot generator driven by said another motor and having a plurality of field-wind ings and an armature, means connecting one of the field windings to a source of control voltage, means connecting another of the windings differentially with respect to said one field: winding for energization in accordance with the armature current of said one motor, a cor-itrolg'en erator energized inaccordance with the output of the pilot generator and with the armature current of said one motor, means responsive to the output of the control generator connected to apply a variable voltage to the said one motor, and means operable to reverse the said another motor and reverse the connections of said another of the pilot generator field windings.

5. A control system for the main motor driving the main rolls of a rolling mill, and a feed roll motor driving rolls for feeding material relative to the main rolls comprising a pilot generator driven by the main motor, said generator being provided with a main field winding connected to a source of substantially constant voltage and a differential field winding energized in accordance with the armature current of the feed roll motor, and means including a control generator cumulatively responsive to the output of the pilot generator and the armature current of the feed roll motor connected to apply a variable voltage to the feed roll motor.

6. In a motor control system, a main motor operable to drive the main rolls of a rolling mill, a feed roll motor connected to drive feed rolls in predetermined relation to the main rolls, means responsive to the speed of the main motor for producing a control voltage variable difierentially with respect to the load on the feed roll motor, a control generator operable to produce a voltage responsive to the output of the pilot generator and to the load on the feed roll motor, and a generator responsive to the output of the control generaotr connected to energize the feed roll motor.

7. In a motor system, a main motor driving the main mill rolls, a pair of feed roll motors driving feed rolls on opposite sides of the main rolls, a pair of pilot generators associated one with each feed roll motor and responsive to the speed of the main mill rolls, said generators having main field windings energized from a source of substantially constant voltage and differential field windings energized in accordance with the armature currents of the associated feed roll motors, a control generator associated with each feed roll motor responsive to the output of the associated pilot generator and the armature current of its associated feed roll motor, draft control means operable to vary the output of the control generators in accordance with the reduction at the main rolls, and means operable to reverse the connections of the pilot generator differential field windings and selectively render one of the draft control means ineffective in accordance with the direction of rotation of the main roll motor.

8. In a control system for controlling a motor in accordance with a reversible variable speed motor, means producing a control voltage responsive to the load on the motor, means including a control generator connected to apply a variable voltage to the motor to be controlled, said control generator having a pattern field winding and a field Winding energized in accordance with the load on the motor, means connected to energize the pattern field Winding including a pilot generator having a driving connection to the reversible variable speed motor, said pilot generator having a main field Winding energized from a source of substantially constant voltage and a differential field winding energized in accordance with the load on the motor, control 10 means effective to reduce the energization of the pattern field winding, and means operable to effect reversal of the reversible variable speed motor, reverse the connections of the differential field Winding and render the control means ineffective.

ALONZO F. KENYON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,264,277 Cook Dec. 2, 1941 2,342,790 Cook Feb. 29, 1944 

